Although she was happy that Karyk was able to solve her problems, she also understood that he was very dangerous! The reason he was turning the citizens wasn't for them to be sacrificed. Instead, it was to create his own army.
The more she thought about it, the more she started to be cautious of him! The man could turn ordinary people into purebloods! He could also kill Purebloods! She didn't know what else he was hiding!
She even felt worried that if he was too strong, he might refuse her request. At any cost, she wanted to win that man over. But as long as she wasn't certain about his loyalty, she couldn't keep him around.
As months passed, Karyk's army increased. The Empress also remembered what Karyk had done to her when he met her! She found out that he had read her memories!